The overall objective of this research is to investigate how channel interactions affect sensitivity to interaural timing differences (ITDs) in adult bilateral cochlear implant users. The number of bilateral cochlear implant patients is increasing rapidly, from 300 to 3000 worldwide in the last three years, and this population could potentially take advantage of ITD information, an important cue for localization and understanding speech in noise that is not preserved by current implant speech processors. In addition, work with this population offers the research community a unique window for evaluating models of human binaural sensitivity. Results of experiments in our lab and other labs using a research processor that allows presentation of specified ITDs indicate good single-channel ITD sensitivity in many bilateral cochlear implant users with postlingual onset of deafness. This project will examine ITD sensitivity in bilateral cochlear implant users under conditions that more closely resemble real-world listening, in which there is interleaved activation of more than one channel, and in which more than one ITD may be presented to the auditory system simultaneously. The proposed program of research is built upon the following two specific aims: 1) to examine how a conflicting ITD affects sensitivity to the ITD of a probe signal, and 2) to examine how the electrode location of an added signal affects sensitivity to the ITD of a probe signal. The proposed experiments represent the first test of channel interactions effects in bilateral cochlear implant hearing. Left-right discrimination and monaural rate discrimination tasks will be used to assess how ITD sensitivity at each cochlear place and overlapping neural activation, respectively, contribute to the elevation of ITD thresholds in the presence of a conflicting ITD. The rate discrimination task anchors these experiments in the existing channel interactions literature, which is exclusively monaural, and the combination of these two tasks provides a basis for separating out monaural from binaural interaction effects. This research has significant public health implications in the area of deafness and communication disorders. Today's bilateral cochlear implant users operate under non-optimal conditions because they listen with two independent processors and there is no obligatory mechanism whereby ITD cues can be captured, preserved and transmitted to the auditory system. Improvements in this area could have important implications for localization and understanding speech in noise in bilateral cochlear implant users. [unreadable] [unreadable] [unreadable]